What do i look for?
Look for a property that will appeal to the largest variety of potential tenants/buyers. Generally, you'll want a "plain" house, one without elaborate banisters, trendy painting, ect. with low maintenence Also, the size of the house, more specifically the number of bedrooms, will be in important factor as well. It is illegal for you to discriminate on a variety of factors when choosing tenants, but if you buy a home with 3 or less bedrooms, you are more likely to have someone living there with few to no children. The reason that it matters is because statistically, homes with no children suffer a fraction of damage/disrepair than a home with 2+ children.
How do i find a tenant?
Well, as having friends/family become your tenant can become extremely sticky, frustrating, irritable situation, I would suggest taking out an ad in the local newspaper/web site, as well as puting a "For Rent" sign up. You'd probably either want to rent to either a stranger or someone who is just an aquintence. When rent come due and you are banging down their door to get it, hard feelings will do nothing but complicate the situation.
Again, what do i look for?
You'll want to pull your potential tenants credit, to see if they have issues paying their bills on time or not. Even if they do, there isn't any guarentee that they will pay you rent on time, but I would imagine that it would be a lot more likely with someone that has good credit. As far as other charactoristics go, make sure that they are they type of people that you want living in your rental. Stability, Cleanliness, previous rental history, criminal record, ect should all be looked into.
What about paperwork to protect me/the house?
Well, you'll need to do the obvious like get Homeowner's insurance on the new home, you'd more than likely want an inspection when you purchase the rental to see if there are any problems with it.
However, you said that you were interested in aquiring more and more properties. One thing I would suggest if forming a Limited Liability Company (LLC). You would have to contact a lawyer to draw up the paperwork, but the grand or two that it takes to get it set up could potentially save everything that you own if a rental goes incredibly wrong. It protects you from being liable from the company... A lawyer would be able to tell you many more benefits of forming one.
Do i need a lawyer?
See above
Anything else?
When you do purchase properties, make sure that you have enough down or the rent is high enough to have a positive cash flow. If you are only going to be picking up 1-2 properties, it won't be that big of an issue, but if you plan on aquiring many of them, you'll want a positive cash flow to help fortify you against any larger expenses that will happen down the road. Also, it is easy to jump in over your head, make sure you start off with a property that you can sustain for a while, just in case you are unable to find a renter immediately.